Polyethylene (PE), waxes and fluorocarbons are still commonly used barrier materials in paper and cardboard products. Environmentally friendly barrier solutions are however gaining more attractiveness for the packaging industry due to environmental aspects. In particular there is a demand for products which are free from barrier materials based on fossil raw-materials. Current market predictions estimate that the market share of water based barrier coating (WBBC) products will increase mainly at the expense of waxes and fluorocarbons but WBBC coating will also replace PE plastic materials.
WBBC coating compositions typically contain an aqueous polymer dispersion and platy minerals such as talcum, cf. for example WO2008141771. Such materials are capable of creating in the coating structures tortuous particle networks which enhance the barrier properties that are principally already obtainable by the application of a binder film on the surface of a substrate.
Various combinations of talc and ground calcium carbonate are disclosed in US2011237730 and WO2008096274.
Talcum or shorter “talc” is a material which is difficult to disperse into water. Furthermore, the talc plates clutter and agglomerate, which means that a significant portion of the talc loading will not contribute to achieving barrier properties. FIG. 1 shows a typical talc coating on a substrate with densely packed particles.